1919-1921: The Irish Republican Army is established in 1919, replacing the Irish Volunteers (which was founded in 1913) as a militant organization fighting for Irish national independence from British rule. The Irish War for Independence (1919-1921) results in the signing of the Anglo-Irish Treaty, which designates Southern Ireland as the Irish Free State, a Member of the British Commonwealth. Northern Ireland, however, remains entirely under British rule.

1937: A new constitution changes the name of the Irish Free State to Ireland, or Eire.

1970s: The Irish Republican Army is revived as a guerilla organization fighting for the reunification of Northern Ireland with Southern Ireland, free from British rule. In response, British forces move into Northern Ireland and impose martial law. During the peak years of violence in Northern Ireland, from 1971-1976, an average of 275 people per year are killed in the conflict. It is during this period of revival in...